Conventional magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk with concentric data tracks, a read/write transducer for reading and writing data on the various tracks, an air bearing slider for holding the transducer adjacent to the track generally in a flying mode above the media, a suspension for resiliently holding the slider and the transducer over the data tracks, and a positioning actuator connected to the suspension for moving the transducer across the media to the desired data track and maintaining the transducer over the data track during a read or a write operation.
In magnetic recording technology, it is continually desired to improve the areal density at which information can be recorded and reliably read. Because the recording density of a magnetic disk drive is limited by the distance between the transducer and the magnetic media, a goal of air bearing slider design is to "fly" a slider as closely as possible to a magnetic medium while avoiding physical impact with the medium. Smaller spacings, or "fly heights", are desired so that the transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk.
In addition to achieving a small average spacing between the disk and the transducer, it is essential that a slider fly at a relatively constant height despite the large variety of conditions it experiences during the normal operation of a disk drive. If the flying height is not constant, the data transfer between the transducer and the recording medium may be adversely affected. It is also essential that variations in the physical characteristics of the slider, due to manufacturing tolerances, not substantially alter the flying height of the slider. If this result is not achieved, the slider's nominal fly height must be increased to compensate for variations between sliders.
An example of a parameter that can vary during normal operation of a disk drive is the radial position of a slider with respect to the rotating disk. The flying height of a slider is affected as the actuator arm is moved radially to access different data tracks. This is due to differences in the linear velocity of the disk at differing radii. In effect, the air bearing slider flies at different speeds at differing radii. Because a slider typically flies higher as velocity increases, there is a tendency for sliders to fly higher at the outer diameter of the disk. Disk drives and sliders must be designed to minimize this effect.
A slider also experiences changes in flying height due to variations in skew. Skew is a measure of the angle formed between the longitudinal axis of the slider and the direction of disk rotation as measured in a plane parallel to the disk. Skew varies in a rotary actuator disk drive as the suspension and attached slider move in an arcuate path across the disk. Skew also varies, to a lesser degree, in a linear actuator disk drive when a resiliently mounted slider moves in response to forces exerted upon it. In addition, skew is a concern due to manufacturing tolerances that may cause a slider to be mounted with a permanent, non-zero skew. For sliders mounted to either type of actuator, non-zero skew values result in a slider being pressurized at a reduced value and therefore flying lower. For this reason, it is important that a slider be relatively insensitive to variations in skew.
A slider also experiences fly height variations due to roll. For a slider with zero skew relative to disk rotation, roll is a measure of the angle formed between the surface of the disk and a plane holding the longitudinal and latitudinal axes of the slider. Variations in roll occur when a resiliently mounted slider experiences a skewed air flow or the actuator experiences a crash stop impact. Insensitivity to roll variations is a crucial requirement of air bearing sliders.
Variations in the crown of a slider can also lead to variations in fly height. Crown is a measure of the concave or convex bending of the slider along its longitudinal axis. Crown develops in sliders because of surface stresses that arise during the fabrication and suspension bonding processes. These stresses are not well controlled and therefore lead to sliders with relatively large variations in crown. Also, an individual slider can experience variations in its crown due to temperature variations that occur during the normal operation of a recording disk drive. For these reasons, it is important that the flying height of a slider not vary substantially as a result of variations in crown. Furthermore, a slider with a non-zero crown is the equivalent of a flat slider flying over a disk having small amplitude, long wavelength undulations. Therefore, since all disks have some degree of waviness, a slider that is less sensitive to variations in crown is also less sensitive to imperfections in the flatness of the recording disk it is flying over.
Finally, a slider experiences varying conditions during the high speed radial movement of the actuator as it accesses data on various portions of the disk. High speed movement across the disk can lead to large values of slider roll and skew and a resultant variation in fly height. This is yet another reason that a slider must be insensitive to changes in roll and skew.
When any of the above described variations in fly height occur, they may result in contact between the slider and the rapidly rotating recording medium. Any such contact leads to wear of the slider and the recording surface and is potentially catastrophic. Prior art slider designs have attempted to avoid this problem by addressing one or more of above described sensitivities, so as to produce a slider with uniform flying height under the varying conditions that may be experienced by the slider.
For example, U.S. Pat. No. 4,894,740 to Chhabra et al. addresses the problem of roll sensitivity by placing a transducing element on the center rail of a three rail slider. This solution, while effective, has the disadvantage of moving the transducing element away from the edge of the slider. Therefore, because a slider only flies correctly when it is more than a certain minimum distance from the outer edge of a rotating disk, those areas of the disk from the center of the slider to the edge of the slider cannot be used. This can result in a loss of 2 to 4% of the usable storage capability of the disk.
Another approach is disclosed in U.S. Pat. No. 4,870,519 to White. White addresses the problem of roll and skew sensitivity by attempting to design a slider that is subjected to very little roll under varying skew conditions. The solution proposed by White requires a well-controlled contour to be placed along corresponding edges of a slider's side rails. These contours can present manufacturing difficulties because they require a controlled etch depth in addition to the traditional process used to create the recess between the rails.
For the foregoing reasons, there is a need for an air bearing slider that maintains a relatively uniform flying height; can accommodate a transducer near its side edge; is insensitive to variations in roll, skew and crown; and does not require additional features that substantially add to the difficulty of manufacturing the slider.